Our long-term objective is to develop new tools for accurate diagnosis of prilnary melanoma and establish criteria for outcome prediction. Diagnosis of in situ melanoma has remained controversial in recent years due to the lack of molecular tools. It is likely that some in situ melanomas may not progress to invasive melanoma, however there are no molecular tools to distinguish between lesions with and without the potential for progression. Similarly, distinction between invasive and invasive/tumorigenic melanolua by conventional histological criteria remains difficult to conduct by general pathologists and is thus controversial. The development of new molecttlar tools for diagnosis has been hampered in melanoma despite the availability of new global gone expression technologies. The paucity of new information is due to the small size of most primary melanomas and the necessity for pathologists to have the entire lesion available for histological analyses. The potential risk for metastatic dissemination and disease progression make it also necessary to have the lesions available for several years before material can be processed for experimental studies. To overcome the limitations of available fresh material from primary melanomas for the development of new markers, our laboratories have embarked on two strategies: 1) Develop an experimental model of melanoma in human skin that closely resembles the pathology of patients' lesions. The lesions are derived from human skin grafted to immunodeficient mice and treated by overexpression of three growth factors and concomitant irradiation with ultraviolet (UV) B. This model allows us to work with fresh and frozen tissues for isolation of RNA without further amplification steps. 2) Develop techniques to identify transcripts and proteins from fixed tissue blocks from archival material no longer required for diagnosis or management. In the proposed investigations we will rely for the initial screening and selection studies on the frozen material from experimentally induced melanomas but will perform verification and validation studies with stored paraffin-embedded material from patients. This biphasic experimental design allows us to use state-of-the-art technologies for a unique molecular dissection of primary human melanoma in order to develop new criteria for diagnosis and outcome prediction. In addition, the requirement for UVB irritation in the xenograft model allows us to evaluate the efficacy of various sunscreen strategies in the prevention of melanoma in the human skin xenografts, which we expect will allow us to validate or suggest modifications to strategies for primary prevention of melanoma.